This invention relates generally to electric motors, and more particularly, to high precision motors for use in lithography systems.
Many precision systems, such as those used in semiconductor manufacturing, use linear or planar motors for positioning objects such as semiconductor wafers. Conventional planar motors are disclosed in U.S. Pat. Nos. 3,851,196, 4,654,571, 5,196,745, and 5,334,892. These patents describe planar motors which have significant limitations. For example, the planar motor of the ""196 patent has a limited range of motion since each motor portion of the stationary magnet array can only generate force in a single direction. Thus, each coil array must always be located above the corresponding magnet array. This limits the range of movement for a given size actuator. The motor disclosed in the ""745 patent similarly requires that each coil array is located above a corresponding linear magnet array. The motor of the ""571 patent includes a coil design which generates only a limited amount of force due to the layout of the coils on the stage. In addition, the design does not generate force in six degrees of freedom. The ""892 patent discloses a planar motor which permits a wide range of motion, but only in a single plane.
Conventional technology also relies upon cumbersome stacked arrangements to achieve six degrees of freedom of movement. These stacked arrangements have a number of drawbacks including additional power requirements, and reduced positioning accuracy. Motors which eliminate stacked arrangements and provide six degrees of freedom over a full range of movement of the wafer stage with a single planar motor typically require large magnet and coil arrays to provide the force required. This results in an increase in mass of the stage and system, thus reducing the natural frequency of the system and degrading performance.
Furthermore, conventional systems often include complex coil geometry which increases the size of the motor and may increase the stage mass, thus increasing power requirements. The complex geometry of the coils often prevents close packing of the coils, which further increases the size of the motor and decreases efficiency. The coil arrays also require a large number of individual coils and amplifiers and complex control electronics to energize the coils and drive the motor.
There is, therefore, a need for a compact motor with a non-complex coil array having closely packed coils, which provides six degrees of freedom with high speed and precision and energy efficient operation.
The present invention overcomes the deficiencies of the prior art by providing a compact motor with a simplified coil geometry which provides six degrees of freedom and energy efficient operation.
The present invention is directed to a planar motor comprising a magnet array having a plurality of magnets with magnetic fields of alternating polarity and a coil array positioned adjacent to the magnet array and operable to interact with the magnetic fields to generate an electromagnetic force between the coil array and the magnet array. The coil array comprises a first linear coil array having a plurality of oval shaped coils extending longitudinally in a first direction, and a second linear coil array having a plurality of oval shaped coils extending longitudinally in a second direction generally orthogonal to the first direction.
The magnets may have a rectangular or octagonal cross-sectional shape, for example. The magnets may be arranged in a checkerboard pattern with alternating magnetic poles along a row or column, or the magnets in one row may have the same polarity with magnets in an adjacent row having oppositely directed polarity, for example.
An exposure apparatus of the present invention generally comprises a frame, an optical system mounted on the frame for imaging a pattern formed in a reticle onto an article, and a base positioned below the optical system. A stage for supporting the article is positioned adjacent to the base. The apparatus further comprises an electric motor operable to move the stage. The motor comprises a magnet array having a plurality of magnets with magnetic fields of alternating polarity, and a coil array positioned adjacent to the magnet array and operable to interact with the magnetic fields to generate an electromagnetic force between the coil array and the magnet array. The coil array includes a first linear coil array having a plurality of oval shaped coils extending longitudinally in a first direction, and a second linear coil array having a plurality of oval shaped coils extending longitudinally in a second direction generally orthogonal to said first direction. One of the coil array and the magnet array is connected to the stage for movement therewith relative to the other of the magnet array and the coil array which is connected to the base.